1. Field of the Invention
The invention relates to an optical device on which an optical element for emitting or receiving light is mounted and a manufacturing method thereof, and a camera module having the optical device mounted thereon.
2. Related Art
With recent improvement in capability of semiconductor devices, the amount of heat that is generated in the semiconductor devices has been increasing, and improvement in heat release efficiency of the semiconductor devices has been greatly demanded. Especially optical devices need to have an optical path above an optical element, and a heat releasing member cannot be provided above the optical element. Therefore, the structure of the optical devices is more disadvantageous in terms of heat release efficiency as compared to other semiconductor devices.
For example, in most image sensor devices, a light receiving element is provided in the center of a silicon chip, a control circuit is provided in the periphery of the chip, and electrode pads are provided on the control circuit, or on and outside the control circuit. In most cases, the chip is mounted on a base made of a ceramic material, resin or the like and having a recessed cross-section by using a paste material, a tape, or the like so that the element formation surface of the chip faces the front. The electrode pads on the chip are connected to electrodes provided within the base through thin gold wires or the like, and the recess of the base is closed by a transparent member such as glass. The recess of the base is generally closed so that the transparent member does not contact the chip surface.
Such an image sensor device mainly releases heat through the following path: heat generated in the control circuit is conducted to the back surface of the chip through the inside of the chip, to the base through the paste material, tape or the like, and to the outside of the image sensor device through the base. The heat thus conducted to the outside of the image sensor device is released through a portion on which the image sensor device is mounted or a heat sink provided in the image sensor device.
With recent increase in the heat generation amount in the control circuit, however, there has been a recognized concern that the above heat release path is not enough to release the heat generated in the control circuit, and high temperature in the control circuit region may cause malfunction or breakdown of the control circuit.
One measure against this is to connect the electrode pads located close to the control circuit to the electrodes within the base by using bumps instead of the thin gold wires. A heat release path can thus be ensured by the bumps, leads and the like having high thermal conductivity efficiency. One example of this type of optical device is shown in FIG. 12. FIG. 12 is a cross-sectional view showing a structure of a conventional optical device.
The optical device of FIG. 12 mainly includes a base 203 and an optical element (image sensor chip) 204. The base 203 has leads 201 sealed in a resin 202 and has a through hole 207 in the center. Each lead 201 has an external terminal 201t at its outer end (each lead 201 is formed by an inner lead and an outer lead). The optical element 204 has a light detecting region 205 in the center. Electrode pads on the optical element 204 are respectively connected to the inner leads of the base 203 through bumps 206. As shown in FIG. 12, each inner lead extends from the center toward a peripheral edge, and is sealed in the resin 202 so that the back surface of the inner lead is exposed in a contact region with the bump 206. As shown in FIG. 12, each outer lead is connected to the respective inner lead and protrudes downward, and no resin is formed on the outer leads. A control circuit (not shown) and the electrode pads are provided outside the light detecting region 205 of the optical element 204. A light shielding film 208 is formed in the periphery of the optical element 204. The light shielding film 208 prevents unnecessary light beams from entering from the back surface of the optical element 204 and prevents dust and the like from entering and adhering to the surface of the optical element 204. In this structure, local heat that is generated in the control circuit on the optical element 204 is conducted from the electrode pads located close to the control circuit to the leads 201 through the bumps 206. An efficient heat release path is thus ensured for this local heat (for example, see Patent document 1: WO1997/005660).
However, the conventional optical device has the following problem:
As shown in FIG. 12, in the conventional optical device, most of the back surface of the optical element 204 is in contact with air, and almost no region of the optical element 204 is in contact with another member. Therefore, the overall heat generated in the optical element is hardly released through a contact region with another member. In other words, a sufficient heat release path cannot be ensured for the overall heat generation in the optical element, causing degradation in the overall heat release efficiency of the optical element.
The same problem also occurs in a hollow-type semiconductor device having a semiconductor element mounted thereon and having the same structure as that of the above optical device. In the hollow-type semiconductor device, most of the back surface of the semiconductor element is in contact with air, and almost no region of the semiconductor element is in contact with another member. Therefore, the overall heat generated in the semiconductor element is hardly released through a contact region with another member. In other words, a sufficient heat release path cannot be ensured for the overall heat generation in the semiconductor element, causing degradation in the overall heat release efficiency of the semiconductor element.